Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds useful behavioral context: it returns counties, cities, zip codes, area type, and tribal codes, and notes the data source (EPA SDWIS Federal Reporting Services Geographic Areas table, US Gov public domain). It doesn't mention pagination or default limits, but the schema covers the limit parameter. The description adds value beyond annotations without contradicting them.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is well-structured and front-loaded with the core purpose. It's a bit longer than strictly necessary, with the use cases and data source adding some redundancy, but every sentence contributes useful context. The filter guidance is clear and the data source attribution is valuable for trust assessment.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The description is complete for a read-only lookup tool. It explains what data is returned, how to filter, and the data source. The output schema exists, so return values don't need explanation. The only minor gap is that it doesn't mention the default limit of 20 or the max of 100, but the schema covers this. Given the tool's simplicity and the rich annotations, this is adequate.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents all four parameters (limit, pwsid, state, county) with examples. The description reinforces the meaning of pwsid, state, and county filters but doesn't add significant new semantics beyond what the schema provides. Baseline 3 is appropriate since the schema does the heavy lifting.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool looks up geographic service areas of EPA-regulated public water systems, listing the returned data (counties, cities, zip codes, area type, tribal codes). It distinguishes itself from sibling tools like sdwis.water.systems, sdwis.water.enforcement, and sdwis.water.violations by focusing on geographic service areas rather than system details, enforcement, or violations.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description explicitly states when to use this tool: 'Filter by state or county to discover which water systems serve a specific area. Filter by PWSID to get all geographic areas served by a specific utility.' It also lists concrete use cases (mapping water service boundaries, identifying utilities for an address, understanding geographic scope of a water quality issue). This provides clear guidance on when to use it versus alternatives.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.